1. Field of the Invention
The present invention relates to a stamp unit provided with a holder which is vertically and slidably disposed in a skirt member and retains a stamp material at the lower side and a grip member which is disposed above the holder and moves it downward, and more particularly to a stamp unit which can improve stamping durability of the stamp material retained at the lower side of the holder against a stamping sheet such as a paper.
Further, the present invention relates to a stamp unit having a stamp material made of porous material with an effective stamping surface capable of stamping and a holder retaining the stamp material at the lower side, and more particularly to a stamp unit which can surely prevent ink leakage from a circumference portion around the effective stamping surface included in a surface of the stamp material exposed from the lower side of the holder.
2. Description of Related Art
Conventionally, the stamp unit of various types has been proposed. One type of the stamp unit is disclosed in Japanese patent application No. Hei 10-52574 which was filed by the present applicant. This stamp unit comprises a grip, a holder, and a skirt member. The holder is connected with the grip so that the holder is vertically movable within the skirt member, and a stamp forming material is disposed at a lower side of the holder.
In the stamp unit, the stamp forming material has a two-layered configuration comprised of an upper layer made of porous hard resin and a lower layer made of porous soft resin in which optical energy absorbing material, such as carbon black, etc., is dispersed. To produce a stamp plate from this stamp forming material by means of a stamp manufacturing device, at first, while a part of rolled-up transparent film is drawn out and fed from the roll, characters and figures are printed on the film through a thermal ink ribbon by a thermal head. Thereby a positive manuscript is formed. Subsequently, the holder with the stamp forming material is set to a predetermined position in the stamp manufacturing device so that the positive manuscript and the lower layer of the stamp forming material are mutually opposed while a transparent acrylic plate exists between the positive manuscript and the stamp forming material. In this state, the lower layer of the stamp forming material is depressed to the transparent acrylic plate. In such the state, when a xenon tube disposed below the transparent acrylic plate is driven to emit light, the lower layer of the stamp forming material is irradiated with the light through the positive manuscript. The part of the lower layer irradiated with light at sites corresponding to the transparent portion of the manuscript is then fused due to heating effect of the optical absorbing material of the lower layer, and solidified. Thereby, the irradiated part is sealed and becomes ink-impermeable. On the other hand, the part of the lower layer corresponding to the characters and the like on the manuscript is not fused-solidified and remains as it is, thus a stamp plate having a stamping surface on a lower face thereof is formed. In the stamping surface, a sealed portion(non-stamping portion) and a non-sealed portion(stamping portion) with a desirable pattern are mixed. The effective stamping surface of the stamp plate is constructed from the above surface in which the stamping portion and the non-stamping portion are mixed. Usually, in the stamp plate, the effective stamping surface corresponds to a flat surface except for the circumference portion along the holder within the surface of the stamp plate.
Further, in the above stamp unit, an ink pack filled with ink can be set in the storage part of the holder, the storage part having a bottom plane on which uneven portions are formed in lattice. When the grip is depressed downward, the ink pack is put between a plate member arranged at the lower end of the grip and the bottom plane of the storage part, thereby the ink pack is broken and opened. The ink flowed out of the opened ink pack is stored in the upper layer and the lower layer of the stamp plate. The ink oozes only from the non-sealed portion on the lower layer of the stamp plate and does not ooze from the sealed portion.
To print characters and the like with the stamp unit, the skirt member of the stamp unit is positioned on a desirable position of the stamping sheet and the grip is depressed downward. Then, the holder moves downward in the skirt member and the stamping surface of the stamp plate is pressed onto the stamping sheet. Thereby, the ink oozes onto the stamping sheet from the non-sealed portion existing in the effective stamping surface of the stamp plate and stamping of characters and the like is conducted onto the stamping sheet. When stamping, it is necessary that the ink does not ooze from the exposed portion except for the effective stamping surface.
However, in the above stamp unit, it is conceivable that tens of thousands of stamping operations are conducted. Therefore, in case that the stamp plate is insufficiently retained to the holder, the ink is apt to ooze from a gap between the holder and the stamp plate. In a more extreme case, the stamp plate comes off the holder.
And if the stamp plate is strongly depressed when stamping, the ink oozes from the circumference portion of the stamp plate. As a result, it concludes that undesirable stamping is conducted.